LANSING — Certain retired teachers could return to the classroom because of a shortage of substitutes and not enough full-time teachers in some subjects under legislation that has cleared the Michigan Senate.

The chamber approved the bill 35-0 Tuesday. A law allowing teachers who retired after mid-2010 to teach again without losing their pension expired nearly 18 months ago.

Reasons for the substitute teaching shortage are varied, including an improved unemployment rate. But school administrators and the companies they contract with for substitutes say retired teachers were snared in legislators' 2012 crackdown on well-paid superintendents retiring, collecting a pension and being rehired by an outside agency to do the same job.

The legislation was sent back to the House, which approved a different version earlier this year.